Major bank HSBC's websites are now all back online, following a denial-of-service (DoS) attack that left customers locked out of their account for nearly 10 hours.

People first began reporting problems accessing us.hsbc.co.uk, hsbc.co.uk and offshore.hsbc.com on Twitter on Thursday at around 5:45pm in the UK, saying they were unable to log in and use the services.

HSBC web services are back up following a DDoS attack. Image: HSBC

Others said they could not get to First Direct's website. First Direct, which does online and telephone banking only, is part of the HSBC group of companies.

On Friday, HSBC said its sites around the world were now back online.

"All HSBC websites have been available since 3am UK time. Thank you for your patience," the bank said in a post to its Twitter account on Friday morning.

According to the bank, its customers' personal details were not compromised in the attack, which disrupted online services but did not affect the other services such as the use of credit cards, debit cards or cash machines.

A hacker with apparent links to Anonymous has laid claim to the attack, and the Izz ad-Din al-Qassam Cyber Fighters group is also suspected of being behind it. The latter, which claims to be a Muslim activist group, made a now-removed post to Pastebin with a timetable of attacks on named financial institutions. Bank of America, Wells Fargo and Ally Financial are among a number of banks to have seen disruption to their sites in the past five weeks, according to reports.

In November 2011, HSBC suffered a major server issue that left customers unable to use cash machines to withdraw money, as well as affecting its HSBC and First Direct websites.